Schizophrenia is a psychiatric illness that has been hypothesized to be due to the over activity of the neurotransmitter dopamine (DA). This hypothesis is based largely on the fact that antipsychotic mediation is able to antagonize the action of DA. Recently it has been demonstrated that there are four forms of human TH that are the result of differential splicing of the TH gene product (1-3). The functional differences between the forms are not known, however it has been proposed that the differences may determine either the intracellular location of the enzyme or the number of phosphorylation sites. However, more recently it has been observed that one of the TH isoforms has a specific activity that is approximately three times greater than one of the other isoforms. It is possible that by expressing the improper form of TH one could account for both an over activity in some brain regions and under activity in other regions as observed in schizophrenic patients. Therefore the studies outlined in this proposal are to map out the distribution of the expression of the four forms of TH mRNA in the CNS of both normals and schizophrenics by in situ hybridization with synthetic oligonucleotides specific for each form. We will further characterize the TH expressing neurons by performing non- isotopic and isotopic double label in situ hybridization with oligonucleotide probes complementary to the TH mRNAs and CCK, SK receptors or D2 autoreceptors. If we do find differences between normals and schizophrenics we would like to study schizophrenics that have never been treated with neuroleptics in order to assess whether or not the changes are due to drug treatment. However it is difficult to obtain completely drug free schizophrenics. Therefore we will need an animal model in which to study the effect of chronic neuroleptic treatment on TH differential splicing so we are planning to investigate whether differential splicing of TH occurs in the cynomolgus monkey. In parallel biochemical studies, we will screen human neuroblastoma cell lines to determine which forms of TH are expressed and whether exogenous factors can regulate the expression of the different forms. We are also planning to stably transfect the human neuroblastoma cells with D2 subtype receptor cDNAs so that we can study the regulation of TH gene expression and splicing mediated by D2 receptors.